1. Field of the Invention
The present invention relates to a waveform data generating apparatus and a waveform data generating method which generate a waveform data applied to, for example, an electronic musical instrument, and relates to a musical tone signal generating apparatus for generating a musical tone signal in accordance with the waveform data generated by the waveform data generating apparatus or the waveform data generating method.
2. Description of the Related Art
It is generally known that in a tone generated by an acoustic musical instrument, play strength causes a tone volume to be changed, and also causes a tone color to be changed. In this specification, the play strength implies the strength of a touch in a case of a keyboard instrument such as a piano and a cembalo, the strength of a rub in a case of a rubbed string instrument such as a violin and a cello, and the strength of a sucked breath in a case of a wind instrument such as a trumpet and a clarinet.
The change of the tone color in accordance with this play strength is mainly caused by levels of respective harmonics (frequency characteristic) constituting the musical tone and envelopes of the respective harmonics, namely, the temporal change of the level of the respective harmonics. For example, as the play strength becomes stronger, levels of high harmonics become higher to accordingly generate brighter tone. Also, as the play strength becomes stronger, a leading edge of the envelope becomes sharper to accordingly generate tone having sharper attack. Moreover, the changing situations of the respective harmonics are different from each other to accordingly generate a complexly changed abundant tone color.
A conventional electronic instrument employs the following techniques in order to simulate the change of the tone color in the above-mentioned acoustic instrument.
In a first technique, n (n is a positive integer) kinds of waveform data generated on the basis of tone generated in accordance with n kinds of different play strengths are stored in a waveform memory. Then, when a key is hit, a waveform data corresponding to the play strength is read out from the waveform memory to generate the tone. However, in this first technique, if the n is small, the tone color is sharply changed in accordance with the play strength. Thus, the change of the tone color becomes unnatural. To smoothly switch the tone color in accordance with the play strength, it is necessary that the n is a very large value. As a result, a large capacity of a waveform memory is required to thereby make the electronic instrument expensive.
In a second technique, m (m is a positive integer and m&lt;n) kinds of waveform data generated on the basis of tone generated in accordance with m different play strengths are stored in the waveform memory. Then, when the key is hit, two kinds of waveform data are selected from the m kinds of waveform data in accordance with the play strength. Then, the selected two kinds of waveform data are interpolated in accordance with the play strength to generate the tone. According to this second technique, an amount of waveform data to be stored in the waveform memory may be smaller than that of the first technique. However, respective phases of the two kinds of waveform data are different from each other. Thus, when the interpolation is done, phase interference is induced to thereby cause the tone color to be damaged.
In a third technique, only one waveform data generated on the basis of tone generated in accordance with strong play strength is stored in the waveform memory. Then, a signal generated in accordance with this waveform data is filtered by such a filter that a characteristic is changed in accordance with the play strength. However, if the play strength is weak the tone color is unnatural in this third technique.
In order to solve the problem of the phase interference in the second technique, Japanese Laid Open Patent Application (JP-A-Showa 60-55398) corresponding to Japanese Examined Patent Application (JP-B-Heisei 5-1480) discloses a waveform generating method in an electronic instrument. However, this waveform generating method only matches phases as an entire waveform. Thus, the phase interference is induced in an individual harmonic, which results in a problem that the tone color is damaged.
Also, the Japanese Laid Open Patent Application (JP-A-Showa 60-55398) corresponding to Japanese Examined Patent Application (JP-B-Heisei 5-1480) discloses a technique of performing a phase matching operation on a first waveform by using a filter, and then generating a second waveform. According to this technique, since the second waveform is generated in accordance with the first waveform, a phase deviation does not occur between both the first waveform and the second waveform. However, the phase matching operation is performed on the first waveform by using the filter. Thus, the envelopes of the respective harmonics included in the second waveform become all equal. Hence, the complex change of the tone color in accordance with the play strength can not be obtained.
Moreover, a method is well known for simulating the change of the tone color by combining the first and third techniques. In this method the waveform data obtained in accordance with the strong play strength and the waveform data obtained in accordance with the weak play strength is actually prepared. Then, any of both the waveform data is selected with certain touch strength as a boundary. However, this method can not obtain the smooth change of the tone color since the respective harmonics are sharply changed.